Membrane filtration processes have long been employed for the selective removal of contaminants and/or salt from water. However, fouling of the membrane filter element limits the through-put rate of conventional tangential-flow filtration (TFF) systems. The lifetime of filter elements, in terms of achievable total through-put flux is similarly limited. This fouling is the result of both concentration polarization and retentate matter. Particularly in the pharmaceutical and bio-industries, these characteristics dictate that filtration/separation processes be batch processes rather than continuous. In batch processes, shutdown for replacement of filtration elements results in loss of extremely valuable residual product materials, expense and time for cleaning and sterilization of systems, and obvious loss of asset utilization productivity.
In the context of industrial processes, such as de-salination, the costs of excess pumping power, maintenance, labor, and materials, can severely impact the economy of production. Further, in the de-salting of drainage waters and of inland waste waters, there may be a volume fee for disposal of the retentate (brine, etc.), and the achievable concentration may be limited by filter membrane fouling.
It has been demonstrated that application of fluid shear in the supply side of a TFF filter element reduces fouling. However, the intuitive act of simply increasing the velocity of feed flow to induce shear results in an associated pressure gradient that manifests as an increased trans-membrane pressure (TMP) at the inlet side that results in further, progressive fouling.